Both fibrin and monocytes are present in lesions of immune mediated tissue damage. The process of fibrin deposition in these lesions may involve monocytes, as these cells respond to many inflammatory stimuli by elaborating potent procoagulant activity (PCA). Indeed, expression of monocyte PCA seems to be an intrinsic part of the immune response as T-lymphocytes are required for recognition of specific stimuli, with subsequent instructions to monocytes. There are also processes which control the persistence of fibrin as it is formed. Monocytes secrete an inhibitor of urokinase (UK-I) which would serve to impede fibrinolysis. Monocyte secretion of UK-1 is augmented by exposure to inflammatory stimuli. It is therefore possible that local expression of monocyte PCA and UK-I are important in the pathogenesis of certain lesions. Indeed, there is an increased incidence of occlusive vascular events in diseases marked by conditions which increase monocyte PCA in vitro. However, monocytes also secrete prourokinase (pro UK). Pro UK derived from non monocyte sources may have plasminogen activator activity. It is not known if monocyte secretion of pro UK is influenced by inflammatory stimuli. The balance between the above activities would therefore be important. The studies outlined herein propose to use methods operative in our lab or published in the literature to: i) determine whether synthesis and secretion of pro UK by human monocytes is influenced by inflammatory stimuli (assay by quantitative Western blotting, use of 3/H-Leucine to discern changes due to synthesis vs secretion of preformed pro UK) ii) determine cellular interactions and metabolic requirements of lymphocyte and monocyte populations in modulation of procoagulant, profibrinolytic, and fibrinolytic inhibitory molecules (using T-cell clones, isolated monocytes and specific assays for each activity); iii) determine relationships in regulation of procoagulant, profibrinolytic, and fibrinolytic inhibitor activities, i.e., how is the "balance" regulated? (Derived from data of the above experiments); iv) determine whether prourokinase elaborated by monocytes is fibrinolytically active or a pro-enzyme (direct measurement of cleavage of 125/I plasminogen to avoid confounding effects of plasmin activation of pro UK to UK. Western blotting of reaction mixtures to identify active (pro) UK as 1 or 2 chains.); and v) determine the effects of binding of urokinase by monocytes on its biologic activity (efficiency as a plasminogen activator, and susceptability to UK- I).